Through-substrate vias and methods for forming the same

ABSTRACT

A device includes a semiconductor substrate and a Metal-Oxide-Semiconductor (MOS) transistor. The MOS transistor includes a gate electrode over the semiconductor substrate, and a source/drain region on a side of the gate electrode. A source/drain contact plug includes a lower portion and an upper portion over the lower portion, wherein the source/drain contact plug is disposed over and electrically connected to the source/drain region. A gate contact plug is disposed over and electrically connected to the gate electrode, wherein a top surface of the gate contact plug is level with a top surface of the top portion of the source/drain contact plug. A Through-Substrate Via (TSV) extends into the semiconductor substrate. A top surface of the TSV is substantially level with an interface between the gate contact plug and the gate electrode.

BACKGROUND

Since the invention of integrated circuits, the semiconductor industryhas experienced continuous rapid growth due to constant improvements inthe integration density of various electronic components (i.e.,transistors, diodes, resistors, capacitors, etc.). For the most part,this improvement in integration density has come from repeatedreductions in the minimum feature size, allowing more components to beintegrated into a given chip area.

These integration improvements are essentially two-dimensional (2D) innature, in that the volume occupied by the integrated components isessentially on the surface of the semiconductor wafer. Although dramaticimprovements in lithography have resulted in considerable improvementsin 2D integrated circuit formation, there are physical limitations tothe density that can be achieved in two dimensions. One of theselimitations is the minimum size needed to make these components. Also,when more devices are put into one chip, more complex designs arerequired.

An additional limitation comes from the significant increase in thenumber and length of interconnections between devices as the number ofdevices increases. When the number and length of interconnectionsincrease, both circuit RC delay and power consumption increase.

Among the efforts for resolving the above-discussed limitations,three-dimensional integrated circuit (3DIC) and stacked dies arecommonly used. Through-silicon vias (TSVs, or sometimes referred to asthrough-substrate vias) are often used in 3DICs and stacked dies forinterconnecting dies. In this case, the TSVs are used to connect theintegrated circuits on a die to the backside of the die. In addition,the TSVs are also used to provide a short grounding path to connect theground in the integrated circuits to the backside of the die, which istypically covered by a grounded aluminum film.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the embodiments, and the advantagesthereof, reference is now made to the following descriptions taken inconjunction with the accompanying drawings, in which:

FIGS. 1 through 9 are cross-sectional views of intermediate stages inthe manufacturing of a Through-Substrate Via (TSV) in accordance withsome exemplary embodiments;

FIG. 10 illustrates a cross-sectional view of a TSV and a MOS device inaccordance with some alternative exemplary embodiments;

FIG. 11 illustrates an intermediate stage in the formation of thestructure shown in FIG. 10; and

FIGS. 12 and 13 illustrate cross-sectional view of intermediate stagesin the manufacturing of a TSV and a MOS device in accordance with yetalternative embodiments.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the embodiments of the disclosure are discussedin detail below. It should be appreciated, however, that the embodimentsprovide many applicable inventive concepts that can be embodied in awide variety of specific contexts. The specific embodiments discussedare illustrative, and do not limit the scope of the disclosure.

A Through-Substrate Via (TSV) and the method of forming the same areprovided in accordance with various exemplary embodiments. Theintermediate stages of forming the TSV are illustrated. The variationsof the embodiments are discussed. Throughout the various views andillustrative embodiments, like reference numbers are used to designatelike elements.

Referring to FIG. 1, wafer 10 is provided. Wafer 10 includes substrate20, which may comprise silicon, silicon germanium, silicon carbon,gallium arsenide, III-V compound semiconductor materials, or the like.Substrate 20 may be a bulk substrate or a Semiconductor-On-Insulator(SOI) substrate. Insulation regions 22, which may be Shallow TrenchIsolation (STI) regions, are formed in substrate 20.

Metal-Oxide-Semiconductor (MOS) device (transistor) 24 is formed at atop surface of substrate 20. MOS device 24 includes gate dielectric 25,gate electrode 26, and gate spacers 27 on the sidewalls of gatedielectric 25 and gate electrode 26. Source and drain regions 28(referred to as source/drain regions hereinafter) may be portions ofsubstrate 20 that are doped with a p-type or an n-typed impurity,depending on the conductivity type of the respective MOS device 24.Source/drain regions 28 may also comprise stressors for applyingstresses to the channel region of MOS device 24, wherein the stressorsmay be silicon germanium stressors or silicon carbon stressors. Althoughnot shown, source/drain silicides may be formed as the top portions ofsource/drain regions 28, and/or the top portion of gate electrode 26.Gate electrode 26 may be a metal gate that is formed of metal or metalalloy(s), although gate electrode 26 may also be formed of polysilicon,metal silicides, or the like. Gate electrode 26 is formed in Inter-LayerDielectric (ILD, referred to as ILD0 hereinafter) 30, wherein ILD0 30may be formed of an oxide such as Phospho-Silicate glass (PSG),Boro-Silicate Glass (BSG), Boron-Doped Phospho-Silicate Glass (BPSG),Tetraethyl Orthosilicate (TEOS) oxide, or the like. In some embodiments,gate electrode 26 is formed using a gate-last approach, although thegate-first approach may be adopted. The top surface of gate electrode 26may be level with the top surface of ILD0 30.

Contact plugs 32, which are sometimes referred to as M0_OD1 or MD1, areformed in ILD0 30, and are overlapping and electrically coupled tosource/drain regions 28. In some embodiments, the top surfaces of MD1s32, the top surface of gate electrode 26, and/or the top surface of ILD030 are level with each other.

Referring to FIG. 2, Chemical Mechanical Polish (CMP) stop layer 38 isformed over ILD0 30, gate electrode 26, and MD1s 32. CMP stop layer 38may comprise silicon nitride, silicon oxycarbide, or the like. Next,photo resist 40 is formed over CMP stop layer 38, and is then patterned.MOS device 24 is protected by the remaining portion of photo resist 40.A patterning is then performed to etch CMP stop layer 38, ILD0 30, andsubstrate 20 to form TSV opening 42. In some embodiments, TSV opening 42extends into a center portion of one of STI regions 22 (marked as 22A),so that the remaining portion of STI region 22 encircles TSV opening 42.During the etching, STI regions 22A may be used as an etch stop layer.Alternatively, TSV opening 42 does not penetrate through any of STIregions 22. TSV opening 42 stops at an intermediate level between thetop surface and the bottom surface of substrate 20.

Referring to FIG. 3, photo resist 40 is removed, for example, through anashing step. Next, as shown in FIG. 4, insulation layer 44 is formed onthe top surface of CMP stop layer 38, and extends into TSV opening 42.Insulation layer 44 may be a substantially conformal layer, wherein thehorizontal portions and the vertical portions of insulation layer 44have substantially the same thickness. Insulation layer 44 may comprisesilicon oxide, silicon nitride, silicon carbide, silicon oxynitride,combinations thereof, or multi-layer thereof. Next, diffusion barrierlayer 46, which also act as a glue layer, is blanket formed to cover thesidewalls and the bottom of TSV opening 42. Diffusion barrier layer 46may include titanium, titanium nitride, tantalum, tantalum nitride, andcombinations thereof, and can be formed using Physical Vapor Deposition(PVD), for example. Next, a thin seed layer (not shown) may be blanketformed on diffusion barrier layer 46. The seed layer may include copperor copper alloys, and metals such as tungsten, silver, gold, aluminum,and combinations thereof may also be included. In some embodiments, theseed layer is formed through PVD. In other embodiments, other methodssuch as electro plating or electro-less plating may be used.

Metallic material 48 is then filled into TSV opening 42. TSV 50 is thusformed in TSV opening 42. In various embodiments, metallic material 48includes copper or a copper alloy, although other metals, such asaluminum, silver, gold, and combinations thereof, may also be used. Theformation methods may include electro plating, for example. Metallicmaterial 48 is filled until the top surface of metallic material 48 ishigher than the top surface of CMP stop layer 38.

FIG. 5 illustrates the CMP step for removing excess metallic material48. In some embodiment, the CMP is performed using a slurry that doesnot attack CMP stop layer 38 substantially, and hence the CMP stops onCMP stop layer 38. A further CMP is then performed, for example, using aslurry that attacks CMP stop layer 38. Accordingly, in some embodiments,the top surfaces of MD1s 32 and gate electrode 26 are exposed. In theresulting structure, the top surface of TSV 50 is level with the topsurfaces of MD1 32, the top surface of ILD0 30, and possibly level withthe top surface of gate electrode 26.

Referring to FIG. 6, Contact Etch Stop Layer (CESL) 52 and ILD1 54 areformed. In some embodiments, CESL 52 is formed of silicon nitride orother dielectric materials. ILD1 54 may comprise silicon oxycarbide,TEOS oxide, and/or the like.

Next, FIG. 7 illustrates the formation of gate contact plug 56,source/drain contact plugs 58 (sometimes referred to as M0_OD2 or MD2since they overlap and are connected to MD1s 32). Gate contact plug 56is alternatively referred to as M0_poly 56 since it overlaps and isconnected to gate electrode 26, which sometimes comprises polysilicon.Furthermore, TSV contact plugs 58′ are formed to overlap and connect toTSV 50, and are used as the electrical connection to TSV 50. Contactplugs 56, 58, and 58′ are formed in ILD1 54, wherein contact plug 56 areelectrically coupled to, and may be in physical contact with, gateelectrode 26. Source/drain contact plugs 58 are electrically coupled to,and may be in physical contact with, M0_OD1 32. TSV contact plugs 58′may penetrate through CESL 52 to contact TSV 50. The formation processof contact plugs 56, 58, and 58′ may include forming openings in ILD1 54and CESL 52, filling the openings with an adhesion/barrier layer and ametallic material such as tungsten or copper, and performing a CMP.

It is observed that each of MD1s 32 and the respective overlying MD2s 58in combination form a source/drain contact plug. Since MD1s 32 and MD2s58 are formed in different process steps, there are visible interfacesbetween MD1s 32 and MD2s 58. Furthermore, the edges of MD1s 32 and MD2s58 may not be continuous and smooth.

In subsequent process, as shown in FIG. 8, etch stop layer 60, M0 vias62, and metal lines 64 are formed. Metal lines 64 are collectivelyreferred to as bottom metal layer M1. M0 vias 62 and metal lines 64 areformed in dielectric layer 66, wherein dielectric layer 66 may be formedof a low-k dielectric material having a k value smaller than about 3.0,or smaller than about 2.5, for example. Dielectric layer 66 isalternatively referred to as an Inter Metal Dielectric (IMD) layer, orIMD1.

In some embodiments, M0 vias 62 and metal lines 64 are formed as adual-damascene structure, and hence there is no noticeable interfaceformed between M0 vias 62 and the respective overlying metal lines 64.The dual-damascene structure may include diffusion barrier layer 63(such as Ti/TiN/Ta/TaN) and a copper-containing material over thediffusion barrier layer. When M0 vias 62 and metal lines 64 form dualdamascene structures, the diffusion barrier is not inserted between M0vias 62 and the overlying metal lines 64. In alternative embodiments, M0vias 62 may be formed using a single-damascene process, and metal lines64 may also be formed using a single-damascene process. In yet otherembodiments, M0 vias 62 are not formed, while metal lines 64 are incontact with contact plugs 56 and 58. In subsequent process, more metallayers (not shown) may be formed over metal lines 64. Etch stop layer 68may then be formed, and further metal lines and vias (not shown,represented by dots) may be formed in more dielectric layers toelectrically couple to TSV 50 and contact plugs 56 and 58.

FIG. 9 illustrates the formation of the backside structure that isconnected to TSV 50. In some exemplary formation process, substrate 20is grinded from the backside (the side facing down in FIGS. 8 and 9),until TSV 50 is exposed. Redistribution line/pad 70 is then formed toelectrically couple to TSV 50. Electrical connector 72 may be formed onredistribution line/pad 70. Electrical connector 72 may be a solderball, a copper pillar, or a composite connector including a copperpillar and a solder cap.

FIGS. 10 through 13 illustrate the formation of TSV 50 in accordancewith alternative embodiments. Unless specified otherwise, the materialsand formation methods of the components in these embodiments areessentially the same as the like components, which are denoted by likereference numerals in the embodiments shown in FIGS. 1 through 9. Thedetails of the like components shown in FIGS. 10 through 13 may thus befound in the discussion of the embodiments shown in FIGS. 1 through 9.

Referring to FIG. 10, the top surface of TSV 50 is level with M0_poly 56and MD2s 58. The formation process is similar to the process for formingTSV 50 in FIG. 8, except the formation of TSV 50 is started afterM0_poly 56 and MD2s 58 are formed, and before etch stop layer 60 isformed. For example, FIG. 11 illustrates a cross-sectional view of anintermediate stage in the formation of TSV 50. In these exemplaryembodiments, after the formation of ILD1 54 and M0_poly 56 and MD2s 58,CMP stop layer 38 is formed, and TSV opening 42 is then formed. Next, aninsulation layer, a diffusion barrier layer, and a seed layer (notshown) are formed. A metallic material is then formed to fill the restof TSV opening 42. The process steps and the materials for forming theinsulation layer, the diffusion barrier layer, the seed layer, and themetallic material may be found referring to the embodiments shown inFIG. 4. A CMP is then performed, and hence the TSV 50 as shown in FIG.10 is formed. Next, as also shown in FIG. 10, the overlying front-sidestructures including etch stop layer 60, M0 vias 62, and metal lines 64are formed. Some of M0 vias 62 and metal lines 64 are formed over, andin contact with, TSV 50. A backside grinding is then performed to exposeTSV 50 from the backside of substrate 20, followed by the formation ofredistribution line/pad 70 and electrical connector 72.

FIGS. 12 and 13 illustrate the cross-sectional view of intermediatestages in the formation of TSV 50 in accordance with yet alternativeembodiments. In these embodiments, TSV 50 is formed after the formationof metal lines 64, using essentially the same method as in FIGS. 2through 5. Etch stop layer 68 is then formed. Accordingly, the topsurface of TSV 50 is level with the top surfaces of metal lines 64,which may form dual damascene structures with the underlying vial) 62.More metal lines, vias, and dielectric layers similar to metal lines 64,vias 62, and dielectric layer 66, respectively, may be formed over thestructure shown in FIGS. 12 and 13.

In accordance with embodiments, a device includes a semiconductorsubstrate and a MOS transistor. The MOS transistor includes a gateelectrode over the semiconductor substrate, and a source/drain region ona side of the gate electrode. A source/drain contact plug includes alower portion and an upper portion over the lower portion, wherein thesource/drain contact plug is disposed over and electrically connected tothe source/drain region. A gate contact plug is disposed over andelectrically connected to the gate electrode, wherein a top surface ofthe gate contact plug is level with a top surface of the top portion ofthe source/drain contact plug. A TSV extends into the semiconductorsubstrate. A top surface of the TSV is substantially level with aninterface between the gate contact plug and the gate electrode.

In accordance with other embodiments, a device includes a semiconductorsubstrate and a MOS transistor. The MOS transistor includes a gateelectrode over the semiconductor substrate, and a source/drain region ona side of the gate electrode. A source/drain contact plug includes alower portion and an upper portion over the lower portion, wherein thesource/drain contact plug is over and electrically connected to thesource/drain region. A gate contact plug is disposed over, andelectrically connected to, the gate electrode, wherein a top surface ofthe gate contact plug is level with a top surface of the top portion ofthe source/drain contact plug. A TSV extends into the semiconductorsubstrate, wherein a top surface of the TSV is substantially level witha top surface of the source/drain contact plug. An etch stop layer isdisposed over and contacting the TSV. The device further includes a viaand a metal line over the via, wherein the via and the metal line form adual damascene structure. A bottom surface of the via is in contact witha top surface of the gate contact plug. The via extends into the etchstop layer.

In accordance with yet other embodiments, a device includes asemiconductor substrate and a MOS transistor. The MOS transistorincludes a gate electrode over the semiconductor substrate, and asource/drain region on a side of the gate electrode. A source/draincontact plug includes a lower portion and an upper portion over thelower portion, wherein the source/drain contact plug is over andelectrically connected to the source/drain region. A gate contact plugis disposed over and electrically connected to the gate electrode,wherein a top surface of the gate contact plug is level with a topsurface of the top portion of the source/drain contact plug. The devicefurther includes a via and a metal line over the via, wherein the viaand the metal line form a dual damascene structure. A bottom surface ofthe via is in contact with a top surface of the gate contact plug. A TSVextends into the semiconductor substrate, wherein a top surface of theTSV is substantially level with a top surface of the metal line.

Although the embodiments and their advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the embodiments as defined by the appended claims. Moreover,the scope of the present application is not intended to be limited tothe particular embodiments of the process, machine, manufacture, andcomposition of matter, means, methods and steps described in thespecification. As one of ordinary skill in the art will readilyappreciate from the disclosure, processes, machines, manufacture,compositions of matter, means, methods, or steps, presently existing orlater to be developed, that perform substantially the same function orachieve substantially the same result as the corresponding embodimentsdescribed herein may be utilized according to the disclosure.Accordingly, the appended claims are intended to include within theirscope such processes, machines, manufacture, compositions of matter,means, methods, or steps. In addition, each claim constitutes a separateembodiment, and the combination of various claims and embodiments arewithin the scope of the disclosure.

What is claimed is:
 1. A device comprising: a semiconductor substrate; aMetal-Oxide-Semiconductor (MOS) transistor comprising: a gate electrodeover the semiconductor substrate; and a source/drain region on a side ofthe gate electrode; a source/drain contact plug comprising a lowerportion and an upper portion over the lower portion, wherein thesource/drain contact plug is over and electrically connected to thesource/drain region; a gate contact plug over and electrically connectedto the gate electrode, wherein a top surface of the gate contact plug islevel with a top surface of the upper portion of the source/draincontact plug; and a Through-Substrate Via (TSV) extending into thesemiconductor substrate, wherein a top surface of the TSV is level withan interface between the gate contact plug and the gate electrode. 2.The device of claim 1 further comprising: an inter-layer dielectric overthe semiconductor substrate, wherein the gate electrode and the lowerportion of the source/drain contact plug comprise portions in theinter-layer dielectric; and an etch stop layer over and contacting theinter-layer dielectric, wherein the top surface of the TSV is in contactwith the etch stop layer.
 3. The device of claim 2, wherein the gatecontact plug and the upper portion of the source/drain contact plugpenetrate through the etch stop layer.
 4. The device of claim 1 furthercomprising a via and a metal line over the via, wherein the via and themetal line form a dual damascene structure, and wherein a bottom surfaceof the via is in contact with a top surface of the gate contact plug. 5.The device of claim 4 further comprising: an inter-layer dielectric overthe gate electrode, wherein the upper portion of the source/draincontact plug comprises a portion disposed in the inter-layer dielectric;and an etch stop layer over the inter-layer dielectric, wherein the viaextends into the etch stop layer.
 6. The device of claim 1, wherein theupper portion and the lower portion of the source/drain contact plughave a distinguishable interface.
 7. The device of claim 1 furthercomprising a TSV contact plug over and contacting the TSV, wherein theTSV contact plug is at a same level as the gate contact plug.
 8. Thedevice of claim 1, wherein the TSV comprises: an insulation layer incontact with the semiconductor substrate; a diffusion barrier layer overthe insulation layer; and a metallic material over the diffusion barrierlayer, wherein each of the insulation layer, the diffusion barrierlayer, and the metallic material extend from the interface into thesemiconductor substrate.